A 2-year-old boy is brought to the emergency department with abdominal pain and bloody diarrhea for the past four days. His parents report that he visited a petting zoo and consumed undercooked hamburgers at a family gathering a week ago. Over the past 12 hours, he has had no urine output, appears fatigued and pale, and has swelling around his eyes. Physical examination reveals: •Pallor, irritability, and periorbital edema •Petechiae on the lower extremities •Blood pressure: 130/85 mmHg (elevated for age) Laboratory findings: •Hemoglobin: 7.5 g/dL (normal: 11-14 g/dL) •Platelets: 90,000/mm³ (normal: 150,000-450,000/mm³) •Blood urea nitrogen (BUN): 60 mg/dL (normal: 6-24 mg/dL) •Creatinine: 2.8 mg/dL (normal: 0.2-0.4 mg/dL) •Blood smear: Numerous schistocytes Question: Which of the following is the most likely causative organism of this patient’s condition?
